Popular and Prevalent

Both describe things that are happen quite frequently.

But,

1st difference, "Popular" always has a positive meaning to it; it is something people enjoy or like doing, whereas "prevalent" can have both a negative (often)or a positive meaning.

2nd difference, "Popular" must have a connection to people; "prevalent" also can include things that happen in the world with no human connection.

----

In some parts of world, earthquakes are prevalent.

In some parts of world, crime is prevalent.

---

To summarize, use ‘popular’ for things that people do, where there is positive feeling; use ‘prevalent’ for things that have a negative feeling or things that happen without any human connection.